Radio frequency transmit filter with integrated impedance matching network

Abstract

A transmit filter for a communications device includes a surface acoustic wave (SAW) band-pass filter configured to pass a transmit frequency band and a tunable transmitter impedance matching network in series. The tunable transmitter impedance matching network matches an input impedance of the SAW band-pass filter to the output impedance of a power amplifier over a portion of the transmit frequency band in response to a tuning input.

It is claimed: 
     
       1. A communications device, comprising:
 a transmitter comprising a power amplifier; 
 a transmit filter configured to pass frequencies within a transmit frequency band and reject frequencies within a corresponding receive frequency band; 
 a tunable transmitter impedance matching network coupled between an output of the power amplifier and an input of the transmit filter; 
 a receive filter configured to pass frequencies within the receive frequency band and reject frequencies within the transmit frequency band, an input of the receive filter connected to an output of the transmit filter 
 a tunable receiver impedance matching network coupled between an output of the receive filter and a receiver port for connection to a receiver; and 
 a controller that controls the transmitter to transmit on a selected transmit frequency channel of a plurality of transmit frequency channels within the transmit frequency band and provides a first tuning input to the tunable transmitter impedance matching network and a second tuning input to the tunable receiver impedance matching network, wherein 
 the first tuning input tunes the tunable transmitter impedance matching network to match an input impedance of the transmit filter to an output impedance of the power amplifier at the selected transmit frequency channel. 
 
     
     
       2. The communications device of  claim 1 , wherein the first tuning input comprises one or more of an analog signal, a digital signal, and a digital bit stream. 
     
     
       3. The communications device of  claim 1 , wherein the transmit filter and the tunable transmitter impedance matching network in series have lower insertion loss from the output of the power amplifier to an output of the transmit filter for at least some of the plurality of transmit frequency channels when compared to the transmit filter and a non-tunable impedance matching network in series. 
     
     
       4. The communications device of  claim 1 , wherein
 the output of the transmit filter and the input of the receive filter are coupled to an antenna port for connection to an antenna. 
 
     
     
       5. The communications device of  claim 4 , wherein:
 the output of the transmit filter and the input of the receive filter are coupled to the antenna port through a tunable antenna impedance matching network, and 
 the controller provides a third tuning input to the tunable antenna impedance matching network. 
 
     
     
       6. The communications device of  claim 1 , wherein the the transmit filter, the receive filter, and the tunable transmitter impedance matching network in series provide improved isolation from the output of the power amplifier to an output of the receive filter for at least some of a plurality of receive frequency channels when compared to the transmit filter, the receive filter, and a non-tunable impedance matching network in series. 
     
     
       7. A communications device, comprising:
 a transmitter comprising a power amplifier; 
 a transmit filter configured to pass frequencies within a transmit frequency band and reject frequencies within a corresponding receive frequency band; 
 a tunable transmitter impedance matching network coupled between an output of the power amplifier and an input of the transmit filter; 
 a receive filter configured to pass frequencies within the receive frequency band and reject frequencies within the transmit frequency band, an input of the receive filter connected to an output of the transmit filter; 
 a tunable antenna impedance matching network coupled between the output of the transmit filter and the input of the receive filter and an antenna port for connection of an antenna, and 
 a controller that controls the transmitter to transmit on a selected transmit frequency channel within the transmit frequency band and provides a first tuning input to the tunable transmitter impedance matching and a second tuning input to the tunable antenna impedance matching network, wherein 
 the first tuning input tunes the tunable transmitter impedance matching network to match an input impedance of the transmit filter to an output impedance of the power amplifier at the selected transmit frequency channel. 
 
     
     
       8. The communications device of  claim 7 , wherein the first tuning input comprises one or more of an analog signal, a digital signal, and a digital bit stream. 
     
     
       9. The communications device of  claim 7 , wherein the transmit filter and the tunable transmitter impedance matching network in series have lower insertion loss from the output of the power amplifier to an output of the transmit filter for at least some of the plurality of transmit frequency channels when compared to the transmit filter and a non-tunable impedance matching network in series. 
     
     
       10. The communications device of  claim 7 , wherein the transmit filter, the receive filter, and the tunable transmitter impedance matching network in series provide improved isolation from the output of the power amplifier to an output of the receive filter for at least some of a plurality of receive frequency channels when compared to the transmit filter, the receive filter, and a non-tunable impedance matching network in series. 
     
     
       11. The communications device of  claim 7 , further comprising:
 a tunable antenna receiver matching network coupled between an output of the receive filter and a receive port for connection of a receiver, wherein 
 the controller provides a third tuning input to the tunable receiver impedance matching network.